ZSM-5 and its synthesis using tetrapropylammonium (TPA) cations as a directing agent are disclosed in U.S. Pat. No. 3,702,886. ZSM-5 has also been synthesized with a wide variety of other organic nitrogen directing agents, for example alkyldiamines having 5-6 carbon atoms (U.S. Pat. No. 4,139,600), dimethylethylpropylammonium (DMEPA) cations (U.S. Pat. No. 4,565,681) and 1,2-diaminocylcohexane (U.S. Pat. No. 5,174,977)
U.S. Pat. No. 4,151,189 discloses that ZSM-5, ZSM-12, ZSM-35 and ZSM-38 can be synthesized using primary amines having 2-9 carbon atoms as the directing agent. In particular Example 12 of this patent discloses synthesis of ZSM-5 using ethylamine as the directing agent. Insufficient information is provided in Example 12 to reach a definitive conclusion as to the silica/alumina molar ratio of the reaction mixture but, assuming the sodium aluminate employed was the normal commercially available material containing 25.5% Al.sub.2 O.sub.3, the reaction mixture would have a silica/alumina molar ratio of 50. According to Table 2 of the '189 patent, the product of Example 12 was only 85% crystalline, i.e. was impure, and had a silica/alumina weight ratio of 17, which corresponds to a molar ratio of 29. However, the product analysis data in Table 2 does not charge balance, in that although 0.11 moles of alumina are present, there are only 0.06 moles of N and essentially no Na. This strongly suggests that much of the aluminium in the product composition of Table 2 was not in the ZSM-5 lattice and hence the molar ratio of the ZSM-5 was significantly higher than 29.
In addition, U.S. Pat. No. 5,369,071 discloses that ZSM-5 with silica to alumina molar ratios as low as 20.3 and alpha values as high as 1488 can be synthesized in the presence of n-propylamine from a reaction mixture having a pH 10-14, an OH.sup.- /SiO.sub.2 ratio of 0.1-0.3, an M/SiO.sub.2 ratio of 0.2-0.6 (where M is an alkali or alkaline earth metal) and an H.sub.2 O/SiO.sub.2 ratio of 10-35.
ZSM-11 and its synthesis using tetrabutylammonium cations as a directing agent are disclosed in U.S. Pat. No. 3,709,979, whereas U.S. Pat. No. 4,108,881 describes the synthesis of ZSM-11 in the presence of an alkyldiamine having 7-12 carbon atoms
It is also known from, for example U.S. Pat. No. 4,229,424, to produce intergrowths of ZSM-5 and ZSM-11, that is crystalline materials exhibiting structural features of both zeolites.
To date it has proved extremely difficult to produce ZSM-5 and ZSM-11 with framework silica to alumina molar ratios less than about 20. (See, for example, R. Szostak, Handbook of Molecular Sieves, Van Nostrand Reinhold, NY, N.Y., 1992, pages 520 and 530, respectively.) Framework aluminum sites are responsible for the acid activity of zeolites, and it is desirable for many catalytic uses to be able to produce ZSM-5 and/or ZSM-11 with the highest possible acid activity and hence the lowest possible framework silica to alumina molar ratio.
It is known that the acid activity of a zeolite can be increased by controlled steaming, see U.S. Pat. No. 4,326,994, but such steaming adds an additional step in the catalyst production regime and hence there is a need for a direct synthesis route for producing high activity ZSM-5 and/or ZSM-11.
According to the invention, it has now been found that ZSM-5, ZSM-11 and intergrowths and/or mixtures thereof with extremely high acid activity can be produced using, as a directing agent, a non-cyclic amine having the formula (C.sub.2 H.sub.6 N).sub.n N.sub.m H.sub.q wherein n is 1, 2 or 3; m is 0 or 1; q is 0, 1 or 2 and (n+m+q) is either 2 or 4.
It is to be appreciated that, although ZSM-5 and ZSM-11 are normally synthesized as aluminosilicates, the framework aluminum can be partially or completely replaced by other trivalent elements, such as boron, iron and/or gallium, and the framework silicon can be partially or completely replaced by other tetravalent elements such as germanium.